Process of making alkyl acrylates



Patented Mar. 15, 1949 amines:

PROCESS OFFMAKING ALKYLACRYLATES Francis Clarke Atwood, Newton, Mass, assignor to Atlantic-Research Associates; Inc., Newtonville,- Mass, a corporation; of Delaware No Drawing; Application Mareh 11, 1943', Serial No. 4783835 Thepresent invention relates to the convere sienof lactates into the corresponding acrylates; such, forexample, as the formation of. alkyl acrry-lates from alkyl lactates, As set: forth in-.-mycopending application, Serial No. 462,048.1"1led: October-14, 1942, which has become abandoned;- the manufacture of acrylate monomers is of: growing importance commercially and various methods have been proposed by means of which; such manufacture may be expedited.

In; my aforementioned: application, I; have pointed; out: the theoretical. problem involved. to bathe dehydration .of the; lactate by the combination; of 1 the hydroxyl group in. thealpha, position. with the hydrogen; in the beta position toforms. water. In view: of the fact: that the carboxyl; grouprtendsto .make the-bond beween the hyr droxy oxygen. and. the carbon tov which it: is". at tachedistronger than-the other carbon to: carbon hondsinrthe;system, when.the lactate is py y r.

the carbon to carbon: bonds ordinarily-tend to; break ratherthan the. carbon to: oxygen: bond: through. whichwthe hydroxylgroup is attached and there results a decomposition into gases'rat-l're err-than the formation of the acrylata.

As I; have stated, in myaboveeidentifiedycoa. pendingapplication, in. order to accomplish thedehydration-: of the lactate, it has-heretoforepbeen proposed to acetylate thehydroxy group by're-q actingthe lactate with acetic anhydride or ketene:.. This accomplishes, in. the acetylated, compound; a: weakeningof the bond through oxygen at the: alpha position to such an extent that. the bond:-

. can. be broken upon pyrolysis to. produce the acrylic acid derivative.

Tonaccomplishthis; as described inmy aforee said'copending --'application', I may direct the. lactate'and. acetic-anhydride-into a pyrolysis furnace either separately or as a mixture and under' such. conditions that no reaction occurs-before-pyrolysis. For example, Imay convert'the lactate-into: the acrylatezby directtpyrolysis and without the; necessity of, theintermediate. conversion of the; lactate? into the acetoxy; propionateby: feeding;

the-lactate and-i acetic anhydride directlyintoythe the cracking'furnace in order to enablethepipes is within the range of 450 to '700'C'., within which.

temperature range lactic acid readily decomposes;

I'have now' discovered that the lactate, and the acetic anhydride may be introduced into the cracking furnace without the presence of lactic acidor other undesirable products by first vaporizing the compounds under suitable conditions andthen'directing'the vapor into the cracking- I find that this may be accomplished:

furnace. by elevating the liquid lactate and acetic anhydride at temperatures well below the range of cracking temperatures above stated, such vaporizingtemperatures being those at which the lactic acid-will remain unvaporized and the conditions:

being such as to minimize or eliminate the decomposition of: thelactic acid; My discovery includes the vaporization, in a similar manner, of other compounds or mixtures of compounds fromv which alkyl acrylates may be formed by cracking atahigh temperatures in the vapor form, such as alkyl alpha-acetoxy propionates (acetylated lactates) alone or in admixture with acetic acid or alkyl acetates. The method is particularly advantageouswhen it isdesired to vaporizesimultaneously two materials which have widely separated boiling points;

The present invention, accordingly, has for an object the provision of, a method by means of which a compound orcoinpounds may be introduced into a. pyrolyzing furnace to form alkyl acrylates, such as methyl acrylate, ethyl acrylate,

etc., without the inclusion of other compounds suchvas; lactic;acid-.which.give rise to difiiculties in the pyrolyzing operation such as hereinabove mentioned A further object of the invention is to provide a. method Qfithe-abovezcharacter wherein, by a, suitable preparatoryoperation, a, compound or compounds: to;- be; introduced. intoa pyrolyzing furnacemay. be freesoiiother compounds normally-.- presentthereinand which give rise to diiiiculties:

in:v the, operation, of the ,pyr'olyzing I furnace.

The. foregoing objects may be attained bythe initial treatment of the compound or compounds toebepyrolyzeddn; such fashion that they are vaporizedand'the vapors, freed of the objectionable. compounds; are then introduced into the pyrolyzing furnace. The attainment of these ob jects isaccomplished more specifically by the flashing: of; the lactate and the companion com. pound; such; as-acetic anhydride, at temperatures:

below pyrolyzing temperatures and Within a. range such that the lactic acid will not be decomposed or at least its decomposition minimized. The flashed compounds are then directed into the pyrolyzing chamber and the cracking operation performed, thus avoiding the formation of coke in the crackin furnace due to the decomposition of the lactic acid.

The process has the additional advantage that the latent heat required for vaporization and the sensible heat necessary to raise the vapors to the temperature in the vaporizing chamber may be supplied from relatively lower temperature sources than that necessary for maintaining the higher temperatures in a cracking furnace. The heat supplied during vaporization need not be supplied by the cracking furnace, thereby increasing the capacity and efliciency of the latter.

In order that the invention may be more fully understood, I Will now proceed to describe, in greater detail, the manner in which it may be realized.

As above stated, before the lactate and the anhydride are introduced into the cracking fur nace Where the temperature may be within the range of 450 to 700 13., I first subject the lactate and the acetic anhydride, or other compound used in the pyrolyzing of the lactate, to a temperature below the cracking temperature for the compounds being flashed and above their boiling point. This temperature may vary with the pressure used. depending upon the requirements of operation.

I find that the compound be flashed at temperatures less than its boiling point temperature under certain conditions, an important factor being to provide a suflicient extent of heated surface and to direct the compound against such surface before it has a chance to boil or agglomerate in large bubbles to any great extent.

The flashing of the lactate and anhydride or other compound may be accomplished, as aforesaid, by directing the liquids into a suitable fluid maintained at a suitable temperature as aforesaid. For example the temperature may be Within the range of 150 to 275 C. at pressures of from 2 to 25 pounds. The fluid used may be aliquid such as an oil having a sufficiently high boiling point to prevent it from being vaporized and carried over with the other vapor into the cracking furnace. The oil will thus contain lactic acid or other compounds that are to be prevented from going over into the cracking furnace and, if the temperature is such that the lactic acid decomposes, the oil thus entrains the coke and other compounds.

In order to provide an operation that is con tinuous, the oil may be circulated continuously and filtered so that the aforesaid compounds may be removed and the oil returned to the circulating system for further heating and use. The lactate and acetic anhydride or other compound may be introduced directly into the oil and the flashed vapors removed and directed into the cracking furnace in any suitable fashion. In an operation that has been performed successfully, the lactate and the anhydride Were-pumped into the flashing chamber under a pressure of 23 to 25 lbs. The operation has been carried out With a destruction of not more than 4% of the mixture introduced into the flashing chamber as non-condensable gases.

As an alternative procedure, I have found that the lactate may be flashed effectively by directing the mixture against a metallic surface of sufficient area and under such conditions that the liquid will be heated by the surface and flash before it has a chance to boil or agglomerate substantially in large bubbles. The residue which does not flash remains as a carbonaceous mass which may be readily removed by a scraper or other appliance. For example, the liquid may be introduced into a pipe having a continuous scraper for removing the carbonaceous material. In order to facilitate the removal of the uni-lashed material, I have found that the surface against which the liquid is directed in order to accomplish its flashing may be initially coated with oil so that the oil will cook into the surface and thus prevent the adherence of the carbonaceous material thereto.

From the foregoing it will thus be seen that the present invention utilizes the operation of first flashing the compounds to be introduced into the pyrolysis chamber under such conditions as to prevent the cracking of such compounds and to enable lactic acid and decomposition. products such as coke, as well as other compounds present in the lactate which is being flashed, from going over into the cracking furnace. The particular manner in which the flashing operation is carried out may van; and the invention is not to be limited save as defined in the appended claims.

I claim:

1. In a method of cracking a lactate to form an acrylate at a relatively high cracking temperature, the steps comprising subjecting a lactate bearing composition from which an alkyl acrylate may be formed by cracking at high temperature to a preliminary and relatively low temperature heating externally of the cracking furnace to vaporize the lactate, separating the lactate vapors from the unvaporized portion of said lactate bearing composition, and then passing the thus separated lactate vapors through a cracking furnace and subjecting them to temperatures suifi-" ciently high to crack the lactate and form an;

perature, the steps comprising subjecting a lac-- tate bearing composition from which an alkyl" acrylate may be formed by cracking at high tem-- perature including an alkyl alpha-acetoxypropionate to a preliminary and relatively low temperature heating externally of the cracking fur-- nace to vaporize the lactate, separating the lactate vapors from the unvaporized portion of said lactate bearing composition, and then passing the thus separated lactate vapors through a cracking furnace and subjecting them to temperatures sufficiently high to crack the lactate and form an acrylate.

3. In a method of cracking a lactate to form an acrylate-at a relatively high cracking temperature, the steps comprising subjecting an alkyl lactate bearing composition from which an alkyl acrylate may be formed by cracking at high temperature to a preliminary and relatively low temperature heating externally of the cracking furnace to vaporize the lactate, separating the lactate vapors from the unvaporized portion of said lactate bearing composition, and then passing the thus separated lactate vapors through a cracking furnace and subjecting them to tem--' peratures sufliciently high to crack the lactate and form an acrylate.

4. In a method of cracking a lactate to form an acrylate at a relatively high cracking temperature, the steps comprising subjecting a. methyl lactate and acetic anhydrlde to a preliminary and relatively low temperature heating externally of the cracking furnace to vaporize the methyl lactate and acetic anhydride, separating the methyl lactate vapors and acetic anhydride vapors from the unvaporized portion and then passing the thus separated lactate and acetic anhydride vapors through a cracking furnace and subjecting them to temperatures sufiiciently high to crack the lactate and form an acrylate.

5. In a method of cracking a lactate to form an acrylate at a relatively high cracking temperature, the steps comprising subjecting a lactate bearing composition from which an alkyl acrylate be formed by cracking at high temperature containing an alkyl lactate and an anhydride to a preliminary and relatively low temperature heating externally of the cracking furnace to vaporize the lactate and anhydride, separating such vapors from the unvaporized portion and then passing the thus separated lactate and anhydride vapors through a cracking furnace and subjecting them to temperatures sufiiciently high to crack the lactate and to form an acrylate.

6. In a method of cracking a lactate to form an acrylate at a relatively high cracking temperature, the steps comprising subjecting a lactate bearing composition from which an alkyl acrylate may be formed by cracking at high temperature to preliminary heating in an oil maintained at a temperature of from 150 to 275 C. whereby to vaporize the lactate, and then separating the vapors thus formed from the unvaporized portion and passing the vapors through a cracking furnace and subjecting th vapors to temperatures of from 450 to 700 C.

7. In a method of cracking a lactate to form an acrylate at a relatively high cracking temperature, the steps comprising subjecting a lactate bearing composition from which an alkyl acrylate may be formed by cracking at high temperature containing an alkyl lactate and an anhydride against a metallic surface at a temperature of between and 275 C. whereby to flash the lactate and anhydride before boiling o1- agglomeration sets in, separating the lactate and anhydride vapors from the unvaporized portion and passing the separated vapors through a cracking furnace separate from said metallic surface and maintained at a temperature sufiiciently high to crack the lactate and to form an acrylate.

FRANCIS CLARKE ATWOOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATlilS PATENTS Number Name Date 2,121,731 Collings June 21, 1938 2,183,357 Ritchie et a1. Dec. 12, 1939 2,265,814 Ritchie et a1. Dec. 9, 1941 2,356,247 Kirk et a1 Aug. 22, 1944 OTHER REFERENCES Rehberg et al.: J. Am. Chem. Soc., vol. 65, June 1943, pages 1003-1006. 

